Ultrasonic wave tomographic imaging system

ABSTRACT

In an ultrasonic wave tomographic imaging system wherein an acoustic image in an object is focused on the ultrasonic wave receiving means by means of an ultrasonic wave lens in order to pick up an image of the desired tomographic plane in the object, the clearness of a tomographic plane image is much improved by a structure wherein the ultrasonic wave is not generated to unwanted regions other than the desired tomographic plane of the object by providing the ultrasonic wave generating means so that scanning occurs only as to the desired tomographic plane of the object, and a gate means is provided so that the ultrasonic wave receiving means can receive an acoustic image corresponding to the scanning in accordance with the scanning of the ultrasonic wave generating means.

BACKGROUND OF THE INVENTION

This invention relates to an ultrasonic wave tomographic imaging systemwhich radiates an ultrasonic wave to an object and reproduces aninternal condition of said object as an image from the reflected thewave, the transmitted wave, refracted wave or the scattered wavereceived from said object, particularly to an ultrasonic wavetomographic imaging system which provides an internal acoustic imagehaving a high S/N ratio.

An ultrasonic wave tomographic imaging system radiates an ultrasonicwave to an object of which the internal condition is to be observed,receives the reflected wave, the transmitted wave or the scattered wavereturning from the inside of said object as an internal acoustic imageof said object and reproduces an internal condition of said object onthe basis of said received waves.

As a system for observing internal condition, an X-ray diagnostic systemis widely used. An ultrasonic wave tomographic imaging system, ascompared with such an X-ray diagnostic system, is especially notdestructive for organs and is less dangerous in the case of a human bodyas an object. Moreover, it has the merit that it is suited for diagnosisof the soft organs of human body.

As an ultrasonic wave tomographic imaging system, the camera systemutilizing an ultrasonic wave lens is already known. This technique isdisclosed in the U.S. Pat. No. 3,937,066 "Ultrasonic Camera System andMethod".

This ultrasonic camera system has the merits that the desired region canbe examined on a real time basis movement of the image can be observed,and the system is superior to the other ultrasonic wave tomographicimaging systems (such as the pulse echo system).

As indicated in FIG. 1, this prior ultrasonic wave tomographic imagingsystem using a camera is composed of the ultrasonic wave generatingmeans (a generator 1) and the ultrasonic wave receiving means (areceiver 2) which are respectively provided on the opposite side of theobject 3.

The generator 1 comprises the ultrasonic wave generator 12 consisting ofan electric-acoustic transducer such as a crystal, etc. housed in thecase 11, and the contact surface 13 of the case 11 to the object iscomposed of a flexible organic film having an acoustic impedance whichis almost equal to that of the object.

The receiver 2 comprises an ultrasonic wave lens 22 which functions asthe ultrasonic wave optical system and an acoustic transducer 23 housedin the case 21, and the contact surface 24 of the case 21 is alsocomposed of an organic film as in the case of said contact surface 13.

The cases 11 and 21 are filled with a medium (for example, water) whichhas an acoustic impedance almost equal to that of the object 3 such as ahuman body 3.

The generator 1 and receiver 2 composed respectively as explained aboveare provided in contact with the object 3 as indicated in FIG. 1, andthe ultrasonic wave generator 12 radiates an ultrasonic wave to theobject 3.

An acoustic image of object 3 by an ultrasonic wave is focused on theacoustic transducer 23 by means of the ultrasonic wave lens 22.

The ultrasonic wave lens 22 converges the ultrasonic waves as is wellknown and focuses an acoustic image at the section X in the locationdetermined by the focal distance of the ultrasonic wave lens 22 and adistance between the ultrasonic wave lens 22 and the acoustic transducer23 thereon.

As the acoustic transducer 23, an acoustic-visual image converter whichutilizes an aluminum suspension liquid or an acoustic-electrictransducer based on the piezoelectric effect can be used.

In the case of the ultrasonic wave tomographic imaging system of thistype, an ultrasonic image of the imaging plane is correctly focused onthe transducer 23 in the ideal case, but actually an ultrasonic waveimage of the plane X is reflected, refracted or scattered until itreaches the surface of transducer 23, and moreover these images aresuperimposed to form an obscured image, or said ultrasonic wave image isdegraded due to the following major causes of noise, namely the spacenoise wherein images of other planes than X plane are superimposed toform an obscured image and the timing noise wherein images aresuperimposed on the image of the plane X with some delay because of themany reflections, refractions and scatterings before they reach thetransducer 23 from the generator 12.

FIG. 2 explains the principle why such space noises are superimposed.The ultrasonic waves that are reflected, refracted or scattered(hereinafter simply referred to as reflected) from the point S on theplane X form an image SA having an obscured space intensity distributionas a result of reflections during the travelling process for focusing atthe point S' on the surface Y of transducer 23.

Similarly, the ultrasonic waves reflected from the point S₃ on the planeX also form a image SD having the obscured space intensity distribution.In addition, the ultrasonic waves reflected from the point S₁ which isnearer to the lens 22 than the plane X are focused to the point S'₁which is further than the surface Y, but form a image SB having theunfocused space intensity distribution at the surface Y.

On the other hand, the ultrasonic waves reflected from the point S₂which is further from the lens 22 than the plane X are focused at thepoint S'₂ which is located before the surface Y and thereby form a imageSC having the diverged space intensity distribution at the surface Y. Asa result, it is a problem to be solved in the ultrasonic wavetomographic imaging system of this type that mutually focused intensitydistributions are superimposed as the space noises of other images andthereby an image is obscured.

FIGS. 3(A) and (B) explain the principle where the timing noises aresuperimposed. The ultrasonic waves reflected from the point S" on theplane X reach the point S"' on the surface Y within a specified time ΔT.On the other hand, the ultrasonic waves reflected from the point S' onthe plane X are also multiply reflected at the reflection surfaces Z₁,Z₂ and reach the point S"' on the surface Y after a delay of ΔT via thepoint S". It is another problem to be solved in the ultrasonic wavetomographic imaging system of this type that the pictures explainedabove are superimposed as in the case of FIG. 3 (B), the illustratedintensity distribution image S'A on the time axis and thereby, theultrasonic waves reflected from the point S' becomes the timing noise,obscuring the image.

SUMMARY OF THE INVENTION

It is an object of this invention to eliminate the space noise or/andtiming noise mentioned above and to improve the S/N ratio in anultrasonic wave tomographic imaging system using a camera system asmentioned above.

It is another object of this invention to improve the S/N ratio with theminimum addition in said ultrasonic wave tomographic imaging systemusing the camera system.

Moreover, it is a further object of this invention to improve saidultrasonic wave tomographic imaging system using the camera system sothat a image plane near to the desired plane can be picked up easilywhile improving the S/N ratio.

This invention involves an ultrasonic wave tomographic imaging systemwherein an acoustic image reflecting from the inside of an object isfocused on the ultrasonic wave receiving means by means of an ultrasoniclens and thereby an image of the desired image plane in said object ispicked up, wherein there is provided means for generating ultrasonicwaves for scanning the desired image plane of said object, and a gatemeans which allows said ultrasonic wave receiving means to receive anacoustic image corresponding to said scanning in accordance with thescanning of said ulrasonic wave generating means.

Moreover, said ultrasonic wave generating, in an embodiment of thisinvention, is characterized in that said ultrasonic wave is generatedfrom the direction along said desired image plane.

In addition, said ultrasonic wave generating means, in an otherembodiment of this invention, is also commonly used as said ultrasonicwave receiving means.

Namely, in this invention the image plane is regionally radiated by theultrasonic wave, while the entire part of said image plane is radiatedin the prior system.

A regional radiation method may be employed in order that the entirepart is at first diagnosed and thereafter the ultrasonic wave isregionally radiated only to the region to be examined carefully, wherebythe space noise of other regions can be alleviated, making clear anultrasonic wave image that is obtained. For example, in the case ofdiagnosis of the nephrolith, the ultrasonic wave is radiated at first tothe entire part in order to obtain the total image and then radiatedonly to the region of the calculus to be examined. Thereby a minutecalculus becomes detectable by limiting the space noises reflected fromthe other regions such as ribs and diaphragm.

Moreover, this regional radiation is useful for combining an image ofthe entire part with less noise by selecting several region images ofthe area to be examined. For this purpose, the tomographic plane isoften scanned spot by spot with an ultrasonic wave or scanned with aflat ultrasonic wave beam.

Moreover, this invention structures an ultrasonic wave receiving meansin order to receive an ultrasonic wave image only of the regionallyradiated area of the tomographic plane. For this purpose, as theultrasonic wave receiving means, a mechanical or electrical space gatemeans is used which synchronizes with the sequential radiation where anultrasonic wave image is received, and an electrical signal of anultrasonic wave is output only from the focusing image planecorresponding to the regional radiation area, for ultrasonic receivingmeans having a two-dimensional and flat plate. In the same way, amechanical space gate means which synchronizes with the sequentialradiation is used for a one dimensional ultrasonic wave receiving means.

Moreover, this invention comprises a timing gate means in the ultrasonicwave receiving means in order to eliminate a timing noise in such a waythat the timing gate means operate in synchronization with the time whenthe ultrasonic wave transmitted from the ultrasonic wave radiation meansreaches the ultrasonic wave receiving means.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the structure of the prior ultrasonic wavetomographic imaging system using a camera method on which this inventionis based.

FIG. 2 explains the space noise of the prior ultrasonic wave tomographicimaging system illustrated in FIG. 1.

FIGS. 3(A) and (B) explain the timing noise of the prior ultrasonic wavetomographic imaging system in FIG. 1.

FIG. 4 and FIG. 5 explain the principle of this invention.

FIG. 6 explains an embodiment of this invention.

FIG. 7 explains the timing noise of the embodiment illustrated in FIG.6.

FIGS. 8(A) to (D) explain the timing gate technique of the embodimentillustrated in FIG. 6.

FIG. 9 and FIG. 10 explain the gate time of the timing gate technique inFIG. 8.

FIG. 11 and FIG. 12 explain electronic focusing techniques used in FIG.4 and FIG. 6.

FIG. 13 explains an embodiment of the gain adjusting technique used inthe structure indicated in FIG. 4.

FIGS. 14(A) to (C) explain another embodiment of the gain adjustingtechnique used in the structure indicated in FIG. 4.

FIG. 15 illustrates the block diagram of an embodiment of thisinvention.

FIG. 16 explains another embodiment of this invention.

FIGS. 17(A) to (C) explain an embodiment of the selective receptiontechnique used in the embodiment of FIG. 16.

FIGS. 18(A) and (B) explain the second embodiment of the selectivereception technique used in the embodiment of FIG. 16.

FIG. 19 explains the third embodiment of the selective receptiontechnique used in the embodiment of FIG. 16.

FIG. 20 and FIGS. 21(A) to (D) explain an embodiment of the tomographicplane changing technique used in this invention.

FIG. 22 indicates a block diagram of the embodiment of FIG. 20.

FIG. 23 explains another embodiment of the tomographic plane changingtechnique used in this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4 and FIG. 5 explain the principle of this invention. In thesefigures, 110 is a generator consisting of at least three rows ofpiezoelectric conversion elements in a matrix; and it can converge theultrasonic wave on the straight line i, for example, by giving a phasedifference to the drive signals for the central row of the piezoelectricconversion elements from that of the two rows on both sides of thecentral row. When this phase difference is varied, the straight line ofthe converged ultrasonic wave moves along the tomographic plane X. Forinstance, said straight line i moves to j. Namely, an electric focusingmethod is employed. When this electric focusing method is also employedfor the row direction of the piezoelectric conversion element matrix,the spot-by-spot scanning becomes possible.

In case a region having different acoustic impedance exists on thestraight line i and j, the focused ultrasonic wave is reflected orscattered and an ultrasonic wave image is transmitted in the verticaldirection to the tomographic plane X. The transmitted ultrasonic waveimage is converged by the ultrasonic wave lens 22 and focused on thetransducer 23 of the image forming surface Y.

This transducer 23 is structured, for example, by piezoelectricconversion element groups arranged in the form at an mxn matrix, and theultrasonic wave pictures of the straight lines i and j in said plane Xare respectively focused on the piezoelectric conversion element groupsof the i-th and j-th rows on the transducer 23.

Therefore, a picture corresponding only to the radiated region can beobtained by employing an electric space gate method so that when theultrasonic wave is radiated to the straight line i, the output of thepiezoelectric conversion element groups in the i-th row is extracted atthe timing that the ultrasonic wave image reaches the transducer 23, andwhile the ultrasonic wave is radiated to the straight line j, the outputof the piezoelectric conversion element groups in the j-th row isextracted.

In addition, it is also possible to employ a mechanical space gatemethod where a mask plate having a slit which makes it possible toreceive an image only at the i-th row position is used when theultrasonic wave is radiated to the straight line i, and which is movedin accordance with the sequential radiation to the tomographic plane.

Similarly, a mechanical space gate means can be used, wherein anultrasonic wave receiving means itself is moved in accordance with thesequential radiation to the tomographic plane, so long as the transducer23 is the one dimensional ultrasonic wave receiving means. What is more,it is certainly possible to use a mechanical space gate means where theimage forming plane is mechanically moved in accordance with a rotatingmotion of the well known acoustic lens system such as an acoustic prismwhich is disclosed in U.S. Pat. No. 3,913,061.

When the ulrasonic wave is radiated regionally only to the region to beexamined, reflection, scattering and refraction from the areas otherthan this region are drastically decreased and a clear image having lessnoise can be obtained.

FIG. 6 outlines an embodiment of this invention and the difference fromthat of FIG. 4 is as follows. FIG. 4 shows an example where theultrasonic wave is radiated from the direction parallel to thetomographic plane X, while FIG. 6 shows an embodiment where theultrasonic wave is radiated from the direction at a right angle to thetomographic plane X.

The electric timing gate mentioned above is more efficient for noiseelimination.

FIG. 7 explains timing noise in the embodiment of FIG. 6. Namely, whenthe reflecting elements 3a, 3c exist in the generator 110 side of theregionally radiated area 3b of an object 3, the reflected wave of thereflecting element 3c is further reflected by the reflecting element 3aand superimposed to the converged ultrasonic wave sent from thegenerator 110 at the radiated area 3b. Thus, the superimposed ultrasonicwaves are transmitted to the acoustic lens 22. This is a kind ofso-called multiple reflections and is a cause of timing noise.

FIGS. 8(A) to (D) explain a transmitting wave and receiving waves. FIG.8(A) shows a transmitting waveform generated from the generator 110,FIG. 8(B) is a receiving waveform before it is electrically gated by thetransducer 23, FIG. 8(C) is a gate signal waveform and FIG. 8(D) gatedreceiving waveform.

As indicated in FIG. 8(B), the multiply reflected waves reach theregionally radiated area 3b with some delay from the not-reflectedradiated wave. In other words, an acoustic output b2 by the multiplyreflected wave is received with some delay from an acoustic output b1 bythe radiated ultrasonic wave.

Therefore, required is to obtain only an output b1 by giving such a gatesignal (FIG. 8 (c)) so as to eliminate acoustic output b2.

The time T₁ from generation to gating can be obtained by dividing thetransmission distance of the ultrasonic wave with the transmission rate.

FIG. 9 explains a method of obtaining this time T₁. The ultrasonic wavegenerated from the generator 110 is transmitted to the direction <x>along the plane to be examined and is reflected at the position x, andthen reaches the position x' on the axis <x> where the transducerexists, having passed the acoustic lens 22.

Let the symbols a, b, L and L' be respectively considered as therelevant distances of each specified cross-section. When thetransmission rate of the ultrasonic wave is considered as C, the time T₁for the cross section at the point x (FIG. 9) is expressed by thefollowing equation. ##EQU1##

In FIG. 9, x'H and x'L respectively indicate the highest and lowestpiezoelectric conversion elements of the matrix, and xH and xL indicaterespectively the reflected points on the <x> axis of the ultrasonicwaves received by the elements of x'H and x'L.

As an embodiment, the radiation method indicated in FIG. 4 is employed.In addition, the above explanation can also be applied to the radiationmethod of FIG. 6.

The graph of FIG. 10 shows the relation between T₁ and x. In this case,parameters are as follows. a=b=50 (cm), c=1.5×10⁵ (cm/sec), L=10 (cm),and L'=20 (cm). As indicated in this graph, the time T₁ from generationof the ultrasonic wave to the gating is determined definitely inaccordance with the position x of the converged area. In addition, theperiod of the gating T₂ is also determined definitely in accordance withthe number of waves and their route differences through the acousticlens.

An electric focusing method for electrically focusing the ultrasonicwaves will be explained below in more detail.

FIG. 11 shows a detailed structure of the generator 110, while FIG. 12shows the driving waveforms.

The one side of the piezoelectric substrate 111 such as crystal orceramic etc. is coated with the common electrode 112 and the other sideis divided into 15 transducers (5×3), each of which has individualelectrodes 113. On the bonding side of the wiring plate 114 which isbonded to individual electrodes, the lead-out electrodes 116 are formedon the positions corresponding to individual electrodes, while on theother side of the wiring plate 114, the wirings V₁ to V₅, M₁ to M₅ andL₁ to L₅ are wired as the printed wirings. Each wiring, in addition, andeach leadout electrode are respectively connected via the through holes115.

When, an in-phase drive signal is applied to the wirings V₁ to V₅ and L₁to L₅, and a delayed drive signal is applied to the wirings M₁ to M₅respectively, the ultrasonic wave is transmitted to the common electrode112 in such a way as to converge to the center from the outer two rows(V₁ to V₅ and L₁ to L₅). At this time, the desired row or focusing lineL where the ultrasonic wave is focused along a single line is determinedby a delay of phase given to the wirings M₁ to M₅. Therefore, thefocusing line L can be moved to the desired position of the tomographicsurface X by adjusting said amount of phase delay. Moreover, thestraight line L is moved over the desired range on the surface X, thereflected waves from the straight lines L with equal intervals aresampled and each wave is sequentially memorized as the data of a singleraster scanning of the display unit. Thereafter, when the stored data isread out and displayed in synchronization with the raster scanning ofthe display unit, display of the desired range on the plane X can bemade with less noise.

In this case, since the ultrasonic wave is attenuated, the received wavebecomes weaker as it becomes farther from the generator. Therefore, thereceiving sensitivity must be changed automatically in accordance withthe distance from the generator along the straight focusing line L.

FIG. 13 explains receiving sensitivity change-over in the embodiment ofthis invention. In this figure, 23a to 23d four rows of receivingelements are shown for simplification of explanation of an example ofthe matrix receiving array. 26a to 26d are amplifiers corresponding tothe receiving elements 23a to 23d. When the ultrasonic wave is focusedto the point A of focal plane X of the object 3 from the generator 110,its acoustic image is focused to the receiving element 23d by means ofthe acoustic lens 22. As explained above, since the intensity of theultrasonic wave is different for the focused points A and B, suchdifference must be corrected at the receiving side. Namely, a gain ofthe amplifier 26a is set in accordance with the distance L₂ from thefocal point A and the generator 110. A gain of the amplifiers 26 b, 26cis similarly set in accordance with the distance between thecorresponding focal point and the generator 110. In this embodiment, thegain of the amplifier 26d is minimum, while the gain of the amplifier26a is maximum. The gain of the amplifiers of each row of the matrixarray is set as explained above.

Here, the gain setting is no longer necessary if intensity difference issuppressed by using a non-linear circuit such as a log-amplifier.

The intensity of the ultrasonic wave becomes independent of the distancefrom the generator along the straight line L by providing generators inthe couple of areas facing each other in the vicinity of the plane X.FIG. 14 shows an example where a couple of opposing generators are used.A couple of generators 110 and 110' like those in FIG. 10 are providedface to face in the vicinity of the plane X.

The focusing line L moves as indicated in FIG. 14 (A) to (C) inaccordance with relation of the timings t₁, t₁₁, t₂ and t₂₁ in FIG. 12where the drive signal is applied to each row of vibrators of a pair ofgenerators 110 and 110'. Since a pair of ultrasonic wave generators arelocated face to face vertically, the sum of the intensity of theultrasonic waves becomes symmetrical and thereby a difference ofintensity due to attenuation can be significantly reduced.

FIG. 15 illustrates the block diagram of an embodiment of thisinvention.

In this figure, 120 is the electronic focusing circuit; this circuitdrives the piezoelectric conversion elements 110a to 110n of thegenerator 110, based on the principle of FIG. 11 and FIG. 12, in view ofthe electronic focusing and scanning. 130 is the scanning positionaddress counter; 140 is the gate signal generator. 150 is the electronicgate circuit, which receives the outputs of the piezoelectronicconversion elements of each row and column of the piezoelectricconversion element array and samples the output of the piezoelectricconversion elements in the specified row with the address signal and theoutput of gate signal generator 140. 160 is the reference clockoscillator; 161 is the 256-bit counter for generating the horizontalsynchronization signal; 162 is the horizontal synchronization signaladdress counter; 163, 164 are the digital-analog converters; and 165,166 are the amplifiers.

The electronic focusing circuit 120 is composed of the RF wave generator121 and drive circuits 122a to 122n for individually driving thepiezoelectric conversion element groups 110a to 110n of each row.

When an output of the horizontal synchronization signal counter 161 isinput, the RF wave generator 121 generates a burst wave consisting of aplurality of sine waves. Usually, two or three waves are used as theburst wave.

The output of the RF wave generator 121 is input to the drive circuits122a to 122n.

The drive circuits 122a to 122n comprise the delay circuits 123a to123n, address memories 124a to 124n, multiplexer circuits 125a to 125nand amplifiers 126a to 126n.

The address memories 124a to 124n are controlled by a count value whichis the output of the address counter 130, and the address counter 130counts the horizontal synchronization signals.

For example, when the number of scanning lines of the display screen isselected to 256, the address counter 130 is a 256-bit counter. Namely,the address counter 130 generates the address from 0 to 255 and thisaddress is the address information of the read-only-memory of theaddress memories 124a to 124n.

The address memories 124a to 124n store the selection signals ofmultiplexer circuits 125a to 125n in individual addresses.

Meanwhile, the burst output the RF wave generator 121 is input to thedelay circuits 123a to 123n. These delay circuits input in parallel tothe multiplexer circuits 125a to 125n the 256 kinds of delayed outputhaving different delay times.

The multiplexer circuits 125a to 125n receive the output ofaforementioned address memories 124a to 124n and output the specifieddelayed output among these delayed outputs.

These delayed outputs are amplified by the amplifiers 126a to 126n andgiven to the individual piezoelectric conversion elements 110a to 110n.Thus, these elements are driven, generating ultrasonic waves.

Namely, each address of the address memories 124a to 124n must store theselection signal for selecting the delayed output in such a way that theultrasonic wave is focused on the area corresponding to the addressspecified by the address counter 130.

The electronic focusing operation is performed as explained above, andthereby the tomographic plane is sequentially scanned.

The gate signal is also generated in synchronization with the electronicfocusing operation by means of the horizontal synchronization signal.

Namely, the gate signal generator 140 comprises the shift register 141,variable time clock generator 142, delay circuit 143, multiplexer 144,address memory 145 consisting of a read only memory and the gate widthset-up circuit 146 consisting of the one-shot multi-vibrator.

The horizontal synchronization signal is delayed by the shift registerand a delay time can be controlled by an output of the variable timeclock generator 142. A delay time of the shift register 141 is soadjusted that the minimum time T₀ of the ultrasonic wave generated fromthe generator 110 required from passing a human body 3 until reachingthe receiving element 23 via the lens is obtained.

The horizontal synchronization signal delayed by the shift register 141is fine-adjusted for its delay time by the delay circuit 143. This delaytime compensates, in case the number of scanning lines (rows) isselected to 256 for example, for a difference of the minimum times insaid scanning operations for every scanning for focusing.

For this reason, the delayed outputs are output in accordance with thescanning lines, for example 256, from the delay circuit 143.

These outputs are input to the multiplexer circuit 144. On the otherhand, the address for focusing and scanning is given from the addresscounter 130. The address register 145 receives the address and outputs aselection signal to the multiplexer circuit 144 in order to select adelayed output which is most suitable for the scanning of the address.

An output of this multiplexer circuit 144 is widened for the timecorresponding to the number of RF waves at the gate width set-up circuit146 and then output as the gate signal.

Meanwhile, the electronic gate circuit 150 is connected to eachpiezoelectric conversion element of the piezoelectric conversion matrix23 of n rows and m columns. The m outputs of the m piezoelectricconversion elements of the first row are input to the receiving circuit151a and then the m outputs of the piezoelectric conversion elements ofthe other rows are sequentially input to the corresponding receivingcircuits with the outputs from the n-th row being input to the receivingcircuit 151n.

The receiving circuits 151a to 151n are respectively composed of thegate circuits 155a to 155n, memory circuits 156a to 156n, multiplexercircuits 157a to 157n. A number m of the gate circuits 155a to 155n andmemory circuits 156a to 156n are respectively provided for the mcolumns. But all the m circuits of each row are indicated as one blockin the figure.

The m gate units of the gate circuits 155a to 155n are given as inputssaid data signals.

The gate circuits 155a to 155n send m receiving inputs by means of thegate signal to the memory circuits 156a to 156n. The m memory units ofthe memory circuits 156a to 156n respectively store the gate outputs.

On the other hand, the address counter 154 of the electronic gatecircuit 150 receives the clocks of the reference clock generator 160,counts them and outputs the counted value. This address counter isdesigned as an m-bit counter (counts each m clock pulses), covering thenumber of columns of the piezoelectric conversion element matrix.

This counted value output is input to the multiplexers 157a to 157n andtherefore the parallel outputs of the multiplexers 157a to 157n areconverted to serial outputs. The memory circuits 156a to 156n are resetby the count-up signal from the address counter 154 for the nextreceiving input.

These n serial outputs are input in parallel to the multiplexer 152. Onthe other hand, the multiplexer 152 receives a counted value of theaddress counter 162 which counts the horizontal synchronization signals.

Therefore, the multiplexer 152 outputs only one serial inputcorresponding to a counted value of the address counter 162 among nserial inputs. The address counter 162 is designed as an n-bit counter(counts every n pulses), covering the n rows of the matrix. Therefore,when the number of scanning lines is selected to be 256, n is selectedto be 256.

An output of this multiplexer 152 is amplified by the amplifier 153 andis used by the display unit as the luminance signal.

Meanwhile, an output of the address counter 162 is converted to ananalog signal by the digital-analog converter 163, amplified by theamplifier 166 and used as the vertical (Y-axis) deflection signal forthe display unit. Similarly, an output of the address counter 154 isalso converted to an analog signal by the digital-analog converter 164,amplified by the amplifier 165 and used as the horizontal (X-axis)deflection signal for the display unit.

The abovementioned operations are summarized below. The drive circuits122a to 122n are controlled so that the ultrasonic waves are focused andscanned to the scanning position of the plane specified by the addresscounter 130, the gate signal which is delayed in accordance with thescanning position specified is generated by the gate signal generator140, each receiving input of the m×n piezoelectric conversion elementmatrix 23 is sampled by this gate signal, the sampled signal isconverted to the serial signal, and thereafter the serial signalcorresponding to the row of the receiving position corresponding to saidscanning position specified by the address counter 162 is output by themultiplexer circuit 152.

In addition to the foregoing description, this invention includes thegenerator and receiver operating with the same unit.

Namely, in this invention, the ultrasonic wave generated from thepiezoelectric converter is deflected and focused by the acoustic lenssystem and an acoustic deflection system and then radiated to the regionof an object to be examined. Thereafter, the ultrasonic wave reflectedfrom such region is in turn deflected and focused again by the acousticlens system and the acoustic deflection system and then received by thepiezoelectric converter.

FIG. 16 illustrates a structure of the second embodiment of thisinvention. In this figure, 22a and 22d are acoustic lenses; 22b and 22care comb-shaped prisms; X₁, X₁ ' is an internal cross-section of anobject and X₂, X₂ ' is a picture forming surface.

In the same figure, a piezoelectric converter is provided vertically tothe paper surface at the position A and then a pair of comb-shapedprisms 22b and 22c are be adjusted so that an acoustic image movesreciprocally in the vertical direction X₁, X₁ ' about the point A'. Whenthe ultrasonic pulses are sequentially generated from the point A, thesepulses are focused and deflected by the lenses 22a and 22d and theprisms 22b and 22c, and then sequentially radiated to each point of thecross-section X₁, X₁ '. In the case when all the piezoelectric elementssend and subsequently receive a pulse together, and adjustment is madeso that each piezoelectric element sends and receives the pulses for anumber of times equal to the number of scanning lines of the displayunit while the prism rotates 180 degrees, so that one full picture canbe obtained when the prism makes a half turn.

In this embodiment, the ultrasonic wave is regionally radiated to thecross-section X₁, X₁ ' of an object, and therefore a strong reflectedwave, resulting in, a clear image can be obtained with less noise due toreflections from the other regions. In addition, a piezoelectricconverter (transducer) is commonly used for transmission and receptionof the ultrasonic wave, thus simplifying the structure of the system.

If the ultrasonic wave transmitted from the point A is focused on thepoint B, the reflected wave does not return to the point A but to theother point a little shifted from the point A, the point C, for example,because a prism already makes a little turn when the reflected wave fromthe point B passes through the prism. Therefore, it is required to use apiezoelectric converter having a sufficient width for covering such ashift of the focusing position. Here, the transmission rate of theultrasonic wave and the rotation speed of the prism are respectivelyconsidered as constant and the shift of the focusing position explainedabove depends on the distance from the prism to the cross-section of theobject and the distance from the prism to the picture forming surface.The aforementioned distances mutually have the following relation,namely when the one becomes shorter, the other becomes longer.Therefore, the shift becomes almost constant when the region to beexamined is deeper or shallower.

This shift can be ignored when a piezoelectric converter is sufficientlywide, but a wider transducer may pick up noise. Therefore, it isdesirable considering the problem mentioned above to provide a controlmeans so that the reflected wave from the cross-section of an object isselectively received only at the focusing position on the piezoelectricconverter. As the above control means, the following three methods canbe employed.

In the first method, as indicated in FIG. 17 (A), a plurality ofconversion units 23a to 23b (7 units in this case) arranged in parallelare used as the piezoelectric converter 23 and a conversion unit locatedin the focusing area is selected electrically in accordance with theshift of the focusing position. Also, the conversion unit as indicatedin FIG. 17 (B) can be used, where the common electrode 311 is providedon one side of a long and slender piezoelectric plate 310, with theindividual electrodes 312 on the projected areas of the other side.Moreover as the electrical selection means, a selection circuit 50 whichsequentially selects the conversion units of the transducer 23 isprovided as indicated in FIG. 17 (C), and thereby a conversion unit isselected for reception in accordance with the rotating angle informationsent from the prism rotating angle detector 40. The received signal issent to the signal processing circuit 60 and converted to a picturesignal therein and displayed on the CRT. Since the shift of the focusingpoints due to the prism changes according to the sine function of thetime, selection by the selection circuit 50 should be made at the timingwhich changes according to the sine function. In this case, it is alsopossible to transmit the ultrasonic wave from the conversion unit 23aand receive it with the conversion units 23a and 23b, or to transmitfrom the units 23a and 23b, and receive with the unit 23a. Whenselective reception is realized by a narrow single conversion unit, anincoming noise can be suppressed outstandingly as compared with thereception with a single piezoelectric converter having a width as wideas seven conversion units.

The second method of the control means is indicated in FIGS. 18(A) and(B), where a slit mechanism is employed. As the piezoelectric converter,a wider conversion unit 35 is used, a mask plate 70 having a slit 75 isprovided in front of said conversion unit, and this mask plate moves inconjunction with the rotating disk 80 by means of the pin 85. Therotating disk 80 rotates in synchronization with a rotation of the prismvia the rotating axis 83 of an electric motor. Therefore, the slit 75makes a reciprocal motion vertically according to the sine function.Each element (shown by the dotted lines) of the conversion unittransmits and receives the ultrasonic wave but selective reception canbe done at the area corresponding to the slit.

The third method of control means is as follow. The focusing point isshifted reciprocally at a constant speed by controlling the rotatingspeed of a prism and a conversion unit is selected at the same timing byusing the piezoelectric converters and the selection circuit means as inthe case of the first method.

Accordingly, a method for controlling the rotating speed of the prism isnow explained. When a prism rotates at a constant speed, the shift ofthe focusing point y on the picture forming surface X₂, X₂ ' can beexpressed by the following equation

    y=A.sub.0 ·sin (W.sub.0 t)                        (1)

where t is time, W₀ is the constant angular speed of the prism and A₀ isan amplitude. If the rotating speed of the prism is considered to be afunction W(t) of time to cause the shift of the focusing point to changelinearly, and if the rotated angle is defined as

    θ(t)=∫W(t)dt,

then it follows that

    y=B.sub.0 ·sin θ(t)=Kt                      (2)

where K is a proportional constant and B₀ is an amplitude, for θ(t)within the range

    0≦θ(t)≦π/2

From equation (2),

    θ(t)=sin.sup.-1 Kt/B.sub.0                           (3)

When the equation (3) is differentiated, the angular speed of the prismas a function of time is:

    W(t)=dθ(t)/dt=1/[(B.sub.0 /K).sup.2 -t.sup.2 ].sup.1/2(4)

Therefore, when t=B₀ /K, W(B₀ /K) from equation (4) is infinite and θ(B₀/K) from equation (3) is π/2. Since it is impossible to make an angularspeed infinite, it is also impossible to linearly control the shift ofthe focusing point y up to the value of π/2 for the rotation angle.Accordingly the value of B₀ is set to be larger than A₀, and y ofequation (2) is considered to change at constant speed until it equalsA₀, and thereafter a different control is provided.

Various kinds of other control methods are possible, for instance, ifrotation is continued with the angular speed being the same as when ybecomes A₀. At this time, the angular speed is given by the followingequation

    [W(t)].sub.(t=A.sbsb.0.sub./K) =[dθ(t)/dt].sub.(t=A.sbsb.0.sub./K) =(K/A.sub.0)/(n.sup.2 -1).sup.1/2                         (5)

    for B.sub.0 =n·A.sub.0 and n>1.                   (6)

The prism rotates through an angle corresponding to y=A₀ during the timeup to t=A₀ /K. Accordingly, from equations (3) and (6),

    θ(A.sub.0 /K)=sin.sup.-1 (1/n)                       (7)

Therefore, the angle for which rotation should be made at a constantspeed within the first quadrant may be expressed as

    π/2-θ(A.sub.0 /K)=π/2-sin.sup.-1 (1/n)         (8)

If the time for a rotating angle θ(t) to change from 0 to π/2 is to beequal to the time π/(2W₀) for a similar rotation at the constant speedW₀, since equation (8) is equal to equation (5) multiplied by[π/(2W₀)-A₀ /K], the following relation is obtained:

    [π/(2W.sub.0)-A.sub.0 /K]·(K/A.sub.0)/(n.sup.2 -1).sup.1/2 =π/2-sin.sup.-1 (1/n), so that K=(2W.sub.0 /π)·A.sub.0 [(n.sup.2 -1).sup.1/2 (π/2-sin.sup.-1 (1/n))+1]        (9)

Equation (9) yields, for n=2,

    K=(2W.sub.0 /π)·A.sub.0 ·(π/3+1)   (10)

The following equation is obtained from substituting equation (10) intoequation (4),

    B.sub.0 /K=2A.sub.0 /K=π/[W.sub.0 (π/3+1)], so that W(t)=[(π/W.sub.0 (π/3+1)).sup.2 -t.sup.2 ].sup.-1/2 (11)

for the range 0≦t≦A₀ /K.

In other areas, the rotation speed should be constant up to the timet=B₀ /K. Analysis can be done in the same manner for times after t=B₀/K. Namely, only the rotation control as expressed by equation (11) isrequired.

FIG. 19 shows an embodiment of a circuit structure for setting forth the3rd method of the control means. The abovementioned rotating angle θ(t)or W(t) is programmed for time in the rotation control circuit 54, andthe pulse motor drive circuit 53 drives a pulse motor 52 in accordancewith such a programmed signal, causing the prisms 22b and 22c to rotateat the programmed rotating speed. During this time, a programmed prismrotating angle data is sent to the selective drive circuit 55 from therotation control circuit 54, and thereby a conversion unit is selectedfor transmission and reception of the ultrasonic wave. The receivedsignal is converted to a picture signal in the signal processing circuit65 and displayed on the CRT 63 through the display control circuit 64.Moreover, this invention is capable of obtaining an acoustic image of adifferent tomographic plane by making use of the regional radiationmethod.

Namely, the ultrasonic wave is regionally radiated to a tomographicplane, an acoustic energy which is almost the same as that radiated tothe region to be examined is radiated, in case the focal depth of thelens is deep, to the regions in the generator side or in the oppositeside in the vicinity of said region to be examined, and therefore a timedifference occurs in the receiving timings of the waves reflected fromthe respective regions. This invention has succeeded in freely changingthe receiving timings using such time difference, and thereby displaysclearly the images of the tomographic plane near to that including theregion to be examined. Therefore, in the present invention, theultrasonic wave receiving means is so structured that only theultrasonic wave image of the regionally radiated area of the tomographicplane can be received. For this purpose, as the ultrasonic wavereceiving means, a functional or electrical space gate means whichsynchronizes with such sequential radiation, so that only the area onthe image forming surface corresponding to the regionally radiated areareceives an ultrasonic picture or outputs an electrical signal of suchultrasonic image, is provided for the two-dimensional and flatultrasonic wave receiving means. In the same way, a mechanical spacegate means which synchronizes with the sequential radiation may be for asingle dimensional ultrasonic wave receiving means.

Moreover, in this invention, the ultrasonic wave receiving meansincludes the timing gate means and space noises are eliminated by thetiming gate means which is designed for operating in synchronizationwith the time required by the ultrasonic wave to reach the ultrasonicwave receiving means from the generator.

FIG. 20 explains the principle of this system. In this figure, 110 isthe generator consisting of at least three lines of a piezoelectricconversion element matrix, and the ultrasonic wave can be focused on theline i, for example, by giving a phase difference to the drive signalsapplied to the center piezoelectric conversion element group and to thetwo lines of piezoelectric conversion element groups on both sides. Itis also possible to move the straight focusing line along thetomographic plane X by changing said phase difference, but in the"Figure 20" it is moved along the plane X by means of the comb-shapedprisms 22b and 22c. For instance, it is moved to the straight line j.Namely, an electrical focusing method is realized. Application of thiselectrical focusing method to the column direction of the piezoelectricconversion element matrix makes possible a spot-by-spot scanning. Inaddition, 25 is is a half mirror, consisting of a polystyrene or acrylicmaterial. 22b and 22c are the acoustic comb-shaped prisms which arerotated mechanically, thereby deflecting the ultrasonic wave generatedfrom the generator 110 so that it is radiated to the specified locationon the tomographic plane X. The generator 110, half mirror 25,comb-shaped prisms 22b and 22c are all housed in the case 21 asindicated in FIG. 1 as in the case of the lens 22 and transducer 23.

If there are regions having different acoustic impedance on the lines iand j of the surface X, the focused ultrasonic wave is reflected orscattered and transmitted in the direction vertical to the surface X.The transmitted wave is converged again by the ultrasonic wave lens 22dand then focused on the transducer 23 provided at the image formingsurface Y.

The transducer 23 is composed, for example, of the piezoelectricconversion elements arranged in the form of an m x n matrix, and theacoustic images of lines in the plane X are respectively focused on thepiezoelectric conversion element groups the on the transducer 23 as inFIG. 19, the transducer operation for example being the same as that ofFIGS. 17(A)-(C).

Therefore, an image corresponding only to the radiated region can beobtained by introducing such an electrical space gate means wherein ifthe line i is radiated, an output of the piezoelectric conversionelement group of the i-th row is extracted at the time when thereflected wave reaches the transducer 23, while if the line j isradiated, an output of the piezoelectric conversion element group of thej-th row is extracted.

In addition, an image of the plane X' which is deeper than the plane Xby a distance Δd can also be obtained by a timing gate means which isdelayed by a time Δt required by the wave to be transmitted for thedistance 2·Δd from the plane X.

Thus, by changing the gate timing of this timing gate means, not onlythe plane X but also a plane which is shifted to the generator side by adistance Δd or the plane X' which is deeper than the plane X can also beobserved by means of the receiving signal of the receiver 23.

FIGS. 21(A) to (D) illustrate the transmitting and receiving waveforms.FIG. 21(A) is the generating waveform of the generator 110. FIG. 21(B)is the receiving wave form of the transducer 23 before it is gatedelectrically. FIG. 21(C) is the gate signal waveform and FIG. 21(D) isthe gated receiving waveform. As indicated in FIG. 21 (B), the multiplereflected waves coming to the regionally radiated area are delayed intiming from the not-reflected wave. Namely, an acoustic output b2 of themultiply reflected wave is delayed as compared with an acoustic outputb1 of the radiated wave.

For this reason, only the acoustic output b1 can be obtained by givingsuch a gate signal C₁ (FIG. 21 (C)) for attenuating an acoustic outputb2. An ultrasonic image of the plane X' is received with a delay time ofΔt.

Therefore, only an output b3 can be extracted by giving the gate signalC₂ after the time T₃.

The time T₁ from generation of the ultrasonic wave to gating can bedetermined by the location of the desired focusing point. In addition,the gating time T₂ can be determined by the number wave and their routedifferences in the acoustic optical system.

FIG. 22 illustrates the block diagram of an embodiment of thetomographic plane changing technique used in this invention.

In this figure, the same portions as those in FIG. 15 are given the samesymbols. 120 is the transmitting drive circuit which drives insynchronization the piezoelectric conversion elements 110a to 110n ofthe generator 110 for transmitting the oscillated ultrasonic waves. 130is the scanning position address counter, and 131 is the scanner driverwhich sequentially rotates the comb-shaped prisms 22b, 22c in accordancewith a value of the address counter 130 for the scanning as indicated inFIG. 20. 140 is the gate signal generator. 150 is the electronic gatecircuit which receives outputs of the piezoelectric conversion elementsof each row and column of the piezoelectric conversion element array andsamples an output of the piezoelectric conversion element of thespecified row with the address signal and an output of the gate signalgenerator 140. 160 is the reference clock generator, 161 is the 256-bitcounter for generating the horizontal synchronization signal, 162 is thehorizontal synchronization signal address counter, 163 and 164 are thedigital-analog converters, 165 and 166 are the amplifiers.

The transmitting drive circuit 120 is composed of the RF wave oscillator121 and the drive circuits 122a to 122n for individually driving thepiezoelectric conversion element groups 110a to 110n.

The RF wave generator 121 generates, when an output of the horizontalsynchronization signal counter 161 is input thereto, a burst wave whichis composed of a plurality of sine waves. Usually two to three RF wavesare used.

An output of the RF wave generator 121 is input to the drive circuits122a to 122n.

The drive circuits 122a to 122n operate as the amplifiers.

The address counter 130 counts the horizontal synchronization signal,which controls the scanner driver 131.

For example, when the number of scanning lines of display screen isselected to 256, The address counter 130 operates as a 256-bit counter.Namely, the address counter 130 generates addresses from 0 to 255 whichbecome the location information of the prisms 22b and 22c.

On the other hand, the burst wave output of the RF wave generator isamplified by the amplifiers 122a to 122n, and is given to thepiezoelectric conversion elements 110a to 110n. Thereby thepiezoelectric conversion elements 110a to 110n are driven, generatingultrasonic waves.

Therefore, the tomographic plane is scanned sequentially while theelectronic focusing operation is carried out during generation of theultrasonic wave to the region corresponding to the address designated bythe address counter 130 when the scanner driver 131 locates the scannerso that the ultrasonic wave is focused thereto.

In synchronization with the electronic scanning operation by thehorizontal synchronization signal, the gate signal is also generated.

Namely, the gate signal generator 140 comprises the shift register 141,the variable time clock generator 142, delay circuit 143, multiplexer144, address memory 145 consisting of a read-only-memory and gate widthset-up circuit 146 consisting of a one-shot multivibrator.

The horizontal synchronization signal is delayed by the shift register141, and a delay time can be controlled by an output of the variabletime clock generator 142. A delay time of the shift register 141 isadjusted so that the ultrasonic wave generated from the generator 110passes on object 3 and reaches the receiving element 23 through the lenswith the minimum time.

A delay time of the horizontal synchronization signal delayed by theshift register 141 is fine-adjusted by the delay circuit 143. This delaytime can be ajusted by compensating for a small difference of theincoming time in individual focusing and scanning in case the scanninglines are 256, for example.

Therefore, the delayed outputs corresponding to the number of thescanning lines, for example, 256 outputs are obtained from the delaycircuit 143.

This output is input to the multiplexer 144. On the other hand, anaddress for focusing and scanning is given from the address counter 130.The address register 145 receives this address and outputs the selectionsignal to the multiplexer 144 in order to select the optimum delayoutput for scanning of this address.

An output of this multiplexer 144 is widened for the width as wide asthe time corresponding to the number of RF waves by the gate widthset-up circuit consisting of the oneshot multivibrator and generated asthe gate signal. This gate signal is input to the variable delay circuit147 and delayed by the abovementioned time Δt. The variable delaycircuit 147 is connected, for example, with the tomographic planesetting circuit 147, By changing the setting of the setting circuit 147,the tomographic plane location can be set from a delay time.

Meanwhile, the electronic gate circuit 150 is connected with thepiezoelectric conversion elements of the matrix 23 of n rows and mcolumns. The m output of the piezoelectric conversion elements in thefirst row are input to the receiving circuit 151a, etc. and the moutputs of the piezoelectric conversion elements in the n-th row areinput to the receiving circuit 151n.

The receiving circuits 151a to 151n are composed of the gate circuits155a to 155n, memory circuits 156a to 156n and multiplexer circuits 157ato 157n. The gate circuits 155a to 155n and memory circuits 156a to 156neach include m circuits, but in the figure they are indicated by onlyone block.

To the m gate units of the gate circuits 155a to 155n the abovementionedgate signals are input.

The gate circuits 155a to 155n output m receiving inputs obtained by thegate signal to the memory circuits 156a to 156n. The m memory units ofthe memory circuits 156a to 156n respectively store the gate outputs.

On the other hand, the address counter 154 of the electronic gatecircuit 150 receives clock pulses of the reference clock generator 160,counts them and outputs a counted value. This address conter 154actually includes a plurality of counters, in number equal to the numberof columns of the piezoelectric conversion element matrix, and isdesigned as an m-bit counter.

The counted values that are output are input to the multiplexers 157a to157n and therefore the parallel outputs of the multiplexers 157a to 157nare converted to the serial outputs. The memory circuits 156a to 156nare reset by a count-up signal of the address counter 154 for the nextreceiving input.

These n serial outputs are input in parallel to the multiplexer 152. Onthe other hand, the multiplexer 152 receives a counted value of theaddress counter 162 which counts the horizontal synchronization signals.

Therefore, the multiplexer 152 outputs only one serial inputcorresponding to a counted value of the address counter 162 among nserial inputs. The address counter 162 is designed as an n-bit counter,covering the n rows of the matrix. Therefore, when the number ofscanning lines is selected to 256, n is selected to 256.

An output of this multiplexer 152 is amplified by the amplifier 153 andis used by the display unit as the luminance signal.

Meanwhile, an output of the address counter 162 is coverted to an analogsignal by the digital-analog converter 163, amplified by the amplifier166 and used as the vertical (Y-axis) deflection signal for the displayunit. Similarly, an output of the address counter 154 is also convertedto an analog signal by the digital-analog converter 164, amplified bythe amplifier 165 and used as the horizontal (X-axis) deflection signalfor the display unit.

The abovementioned operations are summarized below. The drive circuits122a to 122n are controlled so that the ultrasonic waves are focused andscanned to the scanning position of the plane specified by the addresscounter 130, the gate signal which is delayed in accordance with thescanning position specified is generated by the gate signal generator140, a delay time of this gate signal is changed by the variable delaycircuit 147, each receiving input of the m x n piezoelectric conversionelement matrix 23 is sampled by this changed gate signal, the sampledsignal is then converted to the serial signal, and thereafter the serialsignal corresponding to the row of the receiving position correspondingto said scanning position specified by the address counter 162 is outputby the multiplexer circuit 152.

Then, another embodiment of the tomographic plane changing techniquewill be explained.

FIG. 23 illustrates another embodiment of the tomographic plane changingtechnique used in this invention.

The ultrasonic transducer 110 which with an ultrasonic wave generatingmeans is provided in contact with an object 3 in the vicinity of theplane X to be examined of the object 3. As a first means for moving thelens 22 and transducer 23 the movable bae 230 on which is mounted thelens 22 and transducer 23 is manually moved by the handle 235, thesliding base 240 which is in contact with the movable base 230 slidesthereon, and the potentiometer 250 which detects the distance is movedby the movable base 230. As a second means for moving the ultrasonicwave transducer 110, the supporting base 91 supports the ultrasonic wavetransducer, the screw rod 95 is engaged with the screwed hole of thesupporting base 91, the DC motor rotates the screw rod 95 and thepotentiometer 92 detects the location of supporting base 91.

A DC voltage +V_(A) is supplied to the slide resistor 251 in the slidack250 from a voltage regulator 280, while a DC voltage +V_(A) ' issupplied to the slide resistor 94 in the potentiometer 92 from a voltageregulator 96. A voltage V_(B) detected by a sliding terminal 252 whichoperates in conjunction with the handle 235 and a voltage V_(B) 'detected by the sliding terminal 93 which operates in conjunction withthe supporting base 91 are compared at the bridge circuit 290, and avoltage proportional to a difference V_(B) '-V_(B) is supplied to a DCmotor 90.

Here, it is supposed that the two sliding resistors 251 and 94 have thesame resistance value and are homogeneous, and they are arranged in thesame direction as indicated in the figure. When the values of V_(A) andV_(A) ' are set equal and the movable base 230 is set to a certainlocation, the location of the supporting base 91 is determined so thatV_(B) and V_(B') become equal.

At this time, the second moving means as a whole is moved so that theultrasonic wave transducer 1 is accurately located to the position ofthe plane X.

When the acoustic lens 22 and transducer 23 move together with themovable base 230 by means of the handle 135, a value of V_(B) changesand a DC motor rotates until V_(B) ' becomes equal to V_(B) and theultrasonic transducer 110 moves together with the supporting base 91 forthe same distance as mentioned above and in the same direction as themovable base 230. On the other hand, the distance b between the lens 22and transducer 23 is maintained to a constant value during such movementand therefore the location of the tomographic plane X also moves in thesame distance and in the same direction as the movable base 230.Therefore, the ultrasonic transducer 110 is moved accurately to thelocation of the plane X.

In above embodiment, the acoustic lens 22 and transducer 23 movetogether, but it is also possible for changing the location of the planeX to be examined to change the distance b between the acoustic lens 22and transducer 23 by moving the acoustic lens 22 or transducer 23. Inthis case, as the method for responding to the second moving means, amoving distance of the lens or transducer is detected, a new value of bis calculated from the moving distance, a moving distance x of the planeX to be moved is obtained by calculating a distance between the plane Xand the acoustic lens from said value of b and the focal distance of theacoustic lens, and the ultrasonic transducer is moved by the distance x.

These detecting means, calculation means and moving means are all easilyrealized by well known methods.

As explained previously, this invention assures noiseless and cleartomographic plane images by providing a means for generating ultrasonicwave in such a way as to scan the desired tomographic plane of an objectand a gate means which allows the ultrasonic wave receiving means toreceive an acoustic image corresponding to said scanning in accordancewith the scanning by said ultrasonic wave generating means, and inaddition, offers outstanding industrial advantages.

We claim:
 1. An ultrasonic wave tomographic imaging system wherein anacoustic image of a desired tomographic plane in an object is focused onan ultrasonic wave receiving means by an ultrasonic wave lens, saidsystem comprisinggenerating means for generating focused ultrasonicwaves from along a direction that is contained in a plane in space thatincludes said tomographic plane in said object, and for sequentiallyscanning said tomographic plane in said object with said focusedultrasonic waves, said direction being oriented essentially transverselyto the axis of said lens, and a gate means for allowing said ultrasonicwave receiving means to selectively receive the ultrasonic waves of saidacoustic image that are focused by said lens, in correspondence withsaid scanning of said tomograhic plane in said object by said generatingmeans.
 2. The system of claim 1, said generating means comprisingfurther means for generating further focused ultrasonic waves from alongthe opposite direction in said plane containing said desired tomographicplane, for providing in unison said scanning of said tomographic plane.3. The system of claim 1 or 2, comprisingsaid generating means providingsaid scanning by focusing the generated ultrasonic waves effectively insequential rows in said tomographic plane in said object, said receivingmeans comprising at least one respective conversion unit correspondingeffectively to each said row in said tomographic plane, each saidconversion unit of said receiving means comprising plural columnelements for detecting the ultrasonic waves that are focused by saidlens from respective column portions of the corresponding row in saidtomographic plane, and said gate means including means for selectivelyactivating said column elements of each said conversion unit of saidreceiving means in predetermined correspondence to said scanning of saidfocused ultrasonic waves in said tomographic plane, and for selectivelygating in time the outputs of the plural column elements of each saidconversion unit of the receiving mens to selectively detect respectiveportions of said ultrasonic waves of said acoustic image focused by saidlens, wherein the ultrasonic waves received by said receiving meansselectively originate from respective parts of said object in thevicinity of said tomographic plane at which said focusing by saidgenerating means occurs.
 4. The system of claim 3, said receiving meanscomprisingsaid at least one conversion unit with said column elementslocated in the vicinity of said axis of said lens, and a deflectordevice for deflecting the ultrasonic waves focused by said lens ontosaid receiving means in correspondence with said scanning in thetomographic plane with said generating means.
 5. The system of claim 3,said receiving means comprising a plurality of said conversion units,and means for selectively activating said conversion units incorrespondence with said scanning.
 6. The system of claim 3, saidreceiving means including a single one of said conversion units, saidreceiving means comprising a slit mechanism for moving reciprocally infront of the column elements in correspondence with said scanning insaid tomographic plane.
 7. An ultrasonic wave tomographic imaging systemwherein ultrasonic waves from a desired tomographic plane in an objectare focused on an ultrasonic wave receiving means by means of aultrasonic wave lens, said system comprisinggenerating means includingat least one conversion unit for generating ultrasonic waves to befocused by said lens in said tomographic plane for sequentially scanningsaid tomographic plane in said object, gate means for allowing saidultrasonic wave receiving means to selectively receive the ultrasonicwaves focused by said lens onto said receiving means in correspondencewith said scanning of said tomographic plane, said receiving meanscomprising at least said at least one conversion unit of said generatingmeans, a deflector device for deflecting said ultrasonic waves generatedby said first conversion unit for providing said scanning in saidtomographic plane of said object, and each said conversion unitcomprising a plurality of column elements corresponding to respectivecolumn portions in said tomographic plane, wherein said gate meansincludes means for selectively selecting each conversion unit of saidreceiving means for selectively receiving said focused ultrasonic wavesfrom said tomographic plane in correspondence to said scanning thereof,while compensating for the motion of said deflector device during thetravel time of the generated waves until they are received by thereceiving means.
 8. The system of claim 7,said receiving means includinga single one of said conversion units, said gate means comprising amechanical slit apparatus aligned in parallel with the single conversionunit, and connected to move simultaneously across all of said columnelements thereof in correspondence with said scanning of saidtomographic plane, wherein the motion of said slit allows all of saidcolumn elements to selectively generate said ultrasonic waves to befocused by said lens for providing said scanning selectively in saidtomographic plane, and allows said selective reception by said receivingmeans in correspondence to the position of the slit at the time ofreceiving the selectively generated waves.
 9. The system of claim 7,said receiving means comprising a plurality of said conversion unitsaligned in rows, and said gate means including a selector forselectively activating the column portions of at least one of saidplural conversion units at a time, in conjunction with said deflectingof the deflector device, wherein at least one respective one of saidconversion units selectively detects the ultrasonic waves being receivedby said receiving means.
 10. The device of claim 7, 8 or 9, said gatemeans comprising means for selectively gating the detection of theultrasonic waves received by each said conversion unit, so as to varythe position of said tomographic plane in said object along a directionparallel to the axis of said lens.